Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation are complex. Typically, subterranean operations involve a number of different steps such as, for example, drilling the wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation.
When performing subterranean operations, it is often necessary to engage in ancillary operations, such as monitoring the operability of equipment used to perform drilling operations or evaluating the production capabilities of the formation. For instance, it is often desirable to obtain information regarding the formation and/or the fluids therein such as pressure, permeability and composition. The obtained data may then be used to optimize the performance of the subterranean operations. For instance, the data may be used to determine the location and quality of hydrocarbon reserves, whether hydrocarbon reserves can be produced through the wellbore, and for well control during drilling operations. The formation data may be obtained using formation testing tools. The formation testing tools may be used as components of a logging-while-drilling (“LWD”) or measurement-while-drilling (“MWD”) package.
In order to understand the formation testing process, it is important to understand how hydrocarbons are stored in subterranean formations. Typically, hydrocarbons are stored in small holes, or pores, within the subterranean formation. The ability of a formation to allow hydrocarbons to flow between pores and consequently, into a wellbore, is referred to as permeability. Additionally, hydrocarbons contained within a formation are typically stored under pressure. It is therefore beneficial to determine the magnitude of that pressure in order to safely and efficiently produce from the well.
A drilling fluid (“mud”) is typically injected into a wellbore when performing drilling operations. The mud may be water, a water-based mud or an oil-based mud. In some applications, special solids may be suspended in the mud to increase the mud's density. The increase in mud density increases the hydrostatic pressure that helps maintain the integrity of the wellbore and prevents unwanted formation fluids from entering the wellbore. As the mud is circulated in and out of the wellbore during drilling operations, the solids in the mud may be deposited on an inner wall of the wellbore forming a “mudcake.” The thickness of the mudcake may be dependent on the time the borehole is exposed to the drilling fluid.
The mudcake acts as a membrane between the wellbore which is filled with drilling fluid and the hydrocarbon formation. Additionally, the mudcake may hinder the migration of drilling fluids from an area of high hydrostatic pressure in the wellbore to the relatively low-pressure formation.
FIG. 1 depicts the structure and operation of a typical formation tester in accordance with the prior art. In a typical formation testing operation, a wellbore 102 is filled with wellbore fluid or “mud” 104, and the wall of wellbore 102 is coated with a mudcake 106. A formation tester 100 is lowered to a desired depth within the wellbore 102. Once the formation tester 100 is at the desired depth, it is set in place by extending a pair of feet 108 and an isolation pad 110 to engage the mudcake 106. The isolation pad 110 substantially seals against the mudcake 106 and around a probe 112, which places an internal cavity 119 in fluid communication with a formation 122. This creates a fluid pathway that allows formation fluid to flow between the formation 122 and the formation tester 100 while isolated from the wellbore fluid 104.
In order to acquire a useful sample, the probe 112 must stay isolated from the relative high pressure of the wellbore fluid 104. Therefore, the integrity of the seal that is formed by the isolation pad 110 is critical to the performance of the formation tester 100. If the wellbore fluid 104 is allowed to leak into the collected formation fluids, a non-representative sample will be obtained and the test might have to be repeated.
Isolation pads are typically made of rubber and are molded to fit the specific diameter hole in which they will be operating. However, the isolation pads are typically subject to wear and tear. As a result, over time, the sealing capability of the isolation pad is typically compromised, forcing an operator to use valuable rig time to remove the formation tester from the wellbore and replace or repair the isolation pad. Moreover, once the isolation pad is replaced or repaired, the operator typically has to utilize resources to return the formation tester to the location of the sampling where testing was interrupted due to damage to the isolation pad in order to resume testing.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and are not exhaustive of the scope of the disclosure.